1. Field of the Invention
The present invention relates to a system for controlling the air-fuel ratio in an internal combustion engine. The system of the present invention is convenient for use in an automobile engine.
2. Description of the Prior Art
A system for controlling the air-fuel ratio in an internal combustion engine is conventionally known. The system of this type comprises, for example, means for generating a fundamental fuel signal representing an engine fuel request in a steady state of the engine in accordance with values of predetermined engine operation parameters including an engine temperature and representing an engine fuel request; means for detecting a transient state, i.e., acceleration or deceleration, of an engine indicating an output increase request; means, responsive to the measured engine temperature and the detected transient state of the engine, for generating a reinforce promotion signal which has the initial value thereof determined by the detected transient state of the engine and which is increased by a factor changing toward 1 at a rate determined by the measured engine temperature; and means for supplying fuel to the engine in accordance with the fundamental fuel signal and the reinforce promotion signal in accordance with the steady and transient states of the engine. The system provides a fuel supply system which achieves an optimum air-fuel ratio at any time in either a steady state or a transient state of the engine so that the engine continuously operates in an optimum state, as disclosed in for esample, Japanese unexamined Patent Publication (Kokai) No. 56-6034.
In this system, no consideration is given to a change in operating conditions of the engine over a period of time, that is, a change in characteristics due to presence of a deposit which is, for example, a viscous material such as carbon fine particles originating from lubricant components and fuel reaction products at the valve clearance or at an injection nozzle of an EFI injector, a change in characteristics due to presence of such a deposit at the back surface of a cylinder intake valve, and the like. Since the system does not have a means for detecting an air-fuel ratio representing a lean mixture in a transient state of the engine over a period of time, the system cannot prevent a lean mixture from being supplied to the engine in a transient state. This may adversely affect drivability and may, for example, cause an unreliable action in a transient state of the engine. In addition to the above problem, the conventional system is subject to further problems. For example, when an injector is clogged, correction can be made by feedback from an air-fuel ratio sensor when the engine is in the steady state. However, the conventional system does not have a correcting means for providing a similar correction when the engine is in a transient state. Furthermore, similar problems occur due to variations arising during the manufacture of the engines, air flow meters, and the like, or variations arising after the manufacture of these parts.